Posts Tagged ‘pairing’

Lockdown files, otherwise known as pairing records, are well known to the forensic crowd for their usefulness for the purpose of logical extraction. A pairing file created on one computer (the user’s) can be used by the expert to pull information from the iOS device – that, without knowing the PIN code or pressing the user’s finger to unlock the device. Lockdown records do carry their fair share of limitations. For example, their use is severely restricted if the device has just rebooted or powered on and was not unlocked with a passcode afterwards.

Despite that, pairing records have been immensely handy for mobile forensic specialists as they allowed accessing the data in the device without unlocking it with a passcode, fingerprint or trusted face. Specifically, until very recently, lockdown records had never expired. One could use a year-old lockdown file to access the content of an iPhone without a trouble.

To improve security, for a locked iOS device to communicate with USB accessories you must either connect an accessory via lightning connector to the device while unlocked or enter your device passcode while connected, at least once a week.

If you use iAP USB accessories over the Lightning connector (including assistive devices and wired CarPlay) or connect to a Mac/PC, you may therefore need to periodically enter your passcode if you have a passcode set on your iPhone, iPad, or iPod Touch.

As a result, mobile forensic experts can no longer expect lockdown records to survive for periods longer than one week. In order to clearly understand the consequences of this seemingly minor change, let us first look at the pairing records themselves.

Pairing in iOS

In order to enable communications (e.g. file transfers) between the user’s iOS device (iPhone, iPad) and their computer, a trust relationship (or pairing) must be first established. Once a pairing relationship is initially established (by unlocking the iOS device with Touch ID or passcode and confirming the “Trust this computer?” prompt), the two devices exchange cryptographic keys, and the computer is granted trusted access to the iPhone even if the iPhone’s screen is locked.

Even today, seizing and storing portable electronic devices is still troublesome. The possibility of remote wipe routinely makes police officers shut down smartphones being seized in an attempt to preserve evidence. While this strategy used to work just a few short years ago, this strategy is counter-productive today with full-disk encryption. In all versions of iOS since iOS 8, this encryption is based on the user’s passcode. Once the iPhone is powered off, the encryption key is lost, and the only way to decrypt the phone’s content is unlocking the device with the user’s original passcode. Or is it?

The Locked iPhone

The use of Faraday bags is still sporadic, and the risk of losing evidence through a remote wipe command is well-known. Even today, many smartphones are delivered to the lab in a powered-off state. Investigating an iPhone after it has been powered off is the most difficult and, unfortunately, the most common situation for a forensic professional. Once the iOS device is powered on after being shut down, or if it simply reboots, the data partition remains encrypted until the moment the user unlocks the device with their passcode. Since encryption keys are based on the passcode, most information remains encrypted until first unlock. Most of it, but not all. (more…)